Refrigeration system having heat pump and multiple modes of operation

ABSTRACT

The present invention provides a refrigeration system including a first refrigerant circuit including a first heat exchanger for transferring heat from refrigerant, a second refrigerant circuit including a second heat exchanger for transferring heat to refrigerant, and a third refrigerant circuit. The third refrigerant circuit includes a compressor, a condenser connected to the first refrigerant circuit such that heat exchange can occur between the refrigerants of the first and refrigerant circuits, an expansion device, and an evaporator connected to the second refrigerant circuit such that heat exchange can occur between the refrigerant of the second and third refrigerant circuits. The refrigerant can travel along the third refrigerant circuit in a common direction during operation in both heating and cooling modes. Refrigerant can be prevented from moving between first, second, and third refrigerant circuits during operation in heating and cooling modes.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority to U.S. Provisional PatentApplication Ser. No. 60/933,713, filed Jun. 8, 2007, the entire contentsof which is hereby incorporated by reference.

FIELD OF THE INVENTION

The present invention relates to a refrigeration system and a method ofmanufacturing a refrigeration system, and more particularly to arefrigeration system having both an air heating or heat pump mode and anair conditioning or cooling mode.

SUMMARY

In principal, a CO₂ heat pump system can be switched from a heat pump orheating mode (HP) to air conditioning or cooling (A/C) mode by changingthe flow direction in the system cycle so that the A/C mode evaporatoroperates as a HP mode gas cooler, and the A/C mode gas cooler operatesas an HP mode evaporator. However, there are some practical limitationsto this method, which include, but are not limited to, the need forvalves able to accommodate high pressure CO₂, appropriately sizedaccumulators, and heat exchangers in such a system able to withstandhigher system pressures for a fully-reversible system.

In accordance with one feature of the present invention, a refrigerationsystem is provided that can be operated in both HP and A/C modes withoutchanging the general direction of refrigerant flow through the system.This is done by employing two secondary coolant loops, and addingadditional heat exchangers. One desirable application for this system isthe cabin heating and cooling required for truck idle-off. In someembodiments, CO₂ can be used as a refrigerant in at least onerefrigerant circuit.

In some embodiments, the invention provides a refrigeration systemhaving both a heating mode for providing heat to a load space and acooling mode for removing heat from the load space. The system caninclude a first refrigerant circuit including a first heat exchanger fortransferring heat from refrigerant of the first refrigerant circuit toair, a second refrigerant circuit including a second heat exchanger fortransferring heat from air to refrigerant of the second refrigerantcircuit, and a third refrigerant circuit. The third refrigerant circuitcan include a compressor for increasing pressure of refrigerant of thethird refrigerant circuit, a condenser connected to the compressor forreceiving refrigerant from the compressor and connected to the firstrefrigerant circuit such that heat exchange can occur between therefrigerant traveling through the first refrigerant circuit and therefrigerant traveling through the third refrigerant circuit, anexpansion device for reducing the pressure of the refrigerant of thethird refrigerant circuit, and an evaporator connected to the expansiondevice and connected to the second refrigerant circuit such that heatexchange can occur between the refrigerant traveling through the secondrefrigerant circuit and the refrigerant traveling through the thirdrefrigerant circuit. The refrigerant can travel along the thirdrefrigerant circuit in a common direction during operation in both theheating mode and the cooling mode. The refrigerant can be prevented frommoving between the first refrigerant circuit, the second refrigerantcircuit, and the third refrigerant circuit during operation in theheating and cooling modes.

In some embodiments, the present invention provides a refrigerationsystem having both a heating mode for providing heat to a load space anda cooling mode for removing heat from the load space. The refrigerationsystem can include a first refrigerant circuit extending between acompressor, an evaporator, an expansion device, and a condenser. Thefirst refrigerant circuit can define a flow path for a refrigeranttraveling in a direction along the refrigerant circuit during operationof the refrigeration system in the heating mode and the cooling mode.The refrigeration system can also include a second refrigerant circuitextending between the condenser and a heat exchanger, the secondrefrigerant circuit including a first refrigerant pump, and a thirdrefrigerant circuit extending between the evaporator and the heatexchanger. The third refrigerant circuit can include a secondrefrigerant pump. The second refrigerant pump can be operational duringoperation in the heating mode and can be idle during operation in thecooling mode.

The present invention also provides a method of operating arefrigeration system. The method can include the acts of directing arefrigerant along a refrigerant circuit in a direction between acompressor, an evaporator, an expansion device, and a condenser duringoperation of the refrigeration system in a cooling mode, operating afirst pump when the refrigeration system is operating in the coolingmode to circulate refrigerant through a heat exchanger, and transferringheat from a load space to the refrigerant in the refrigerant circuitwhen the refrigeration system is operating in the cooling mode. Themethod can also include the acts of stopping the first pump when therefrigeration system is operating in a heating mode, directing therefrigerant along the refrigerant circuit in the direction duringoperation of the refrigeration system in the heating mode, operating asecond pump when the refrigeration system is operating in the heatingmode to circulate refrigerant through the heat exchanger in heatexchange relation with the refrigerant of the refrigerant circuit, andtransferring heat to the load space from the refrigerant in therefrigerant circuit when the refrigeration system is operating in theheating mode.

Other aspects of the invention will become apparent by consideration ofthe detailed description and accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a schematic illustrating a refrigeration system according tosome embodiments of the present invention and showing the refrigerationsystem operating in a cooling mode.

FIG. 1B is a schematic illustrating the refrigeration system of FIG. 1Aand showing the refrigeration system operating in a heating mode.

FIG. 2A is a schematic illustrating a refrigeration system according toan alternate embodiment of the present invention and showing therefrigeration system operating in a cooling mode.

FIG. 2B is a schematic illustrating the refrigeration system of FIG. 2Aand showing the refrigeration system operating in a heating mode.

FIG. 3A is a schematic illustrating a refrigeration system according toanother alternate embodiment of the present invention and showing therefrigeration system operating in a cooling mode.

FIG. 3B is a schematic illustrating the refrigeration system of FIG. 3Aand showing the refrigeration system operating in a heating mode.

FIG. 4A is a schematic illustrating a refrigeration system according toa yet another alternate embodiment of the present invention and showingthe refrigeration system operating in a cooling mode.

FIG. 4B is a schematic illustrating the refrigeration system of FIG. 4Aand showing the refrigeration system operating in a heating mode.

DETAILED DESCRIPTION

Before any embodiments of the invention are explained in detail, it isto be understood that the invention is not limited in its application tothe details of construction and the arrangement of components set forthin the following description or illustrated in the following drawings.The invention is capable of other embodiments and of being practiced orof being carried out in various ways. Also, it is to be understood thatthe phraseology and terminology used herein is for the purpose ofdescription and should not be regarded as limiting. The use of“including,” “comprising,” or “having” and variations thereof herein ismeant to encompass the items listed thereafter and equivalents thereofas well as additional items.

Unless specified or limited otherwise, the terms “mounted,” “connected,”“supported,” and “coupled” and variations thereof are used broadly andencompass both direct and indirect mountings, connections, supports, andcouplings. Further, “connected” and “coupled” are not restricted tophysical or mechanical connections or couplings.

Also, it is to be understood that phraseology and terminology usedherein with reference to device or element orientation (such as, forexample, terms like “central,” “upper,” “lower,” “front,” “rear,” andthe like) are only used to simplify description of the presentinvention, and do not alone indicate or imply that the device or elementreferred to must have a particular orientation. In addition, terms suchas “first”, “second”, and third” are used herein for purposes ofdescription and are not intended to indicate or imply relativeimportance or significance.

FIGS. 1A and 1B show a schematic illustrating a refrigeration system 10according to some embodiments of the present invention. During operationin an air conditioning or cooling (A/C) mode, refrigerant, such as, forexample, CO₂ leaves a compressor 12 and enters a first evaporator,which, in the illustrated embodiment of FIGS. 1A and 1B, is anair-cooled gas cooler 14. In the embodiment shown in FIG. 1A, the flowof refrigerant is shown by three solid arrows. Depending on one or moreof the operating conditions, the anticipated heating or cooling load,and the type of refrigerant employed, the refrigerant may exit thecompressor in a supercritical state. While reference is made herein tothe use of CO₂ as a refrigerant, in some embodiments, otherrefrigerants, including, but not limited to, water, R12, engine coolant,any other organic refrigerant, R245fa, glycol, air, and the like canalso or alternatively be used. As shown in FIG. 1A, a fan 16 can bepositioned adjacent to or along an airflow path opening onto theair-cooled gas cooler 14 to reject heat from the gas cooler 14 to theambient environment via transfer of heat from the refrigerant to anambient air flow provided by the fan 16.

The refrigerant can then enter a second evaporator, which, in theillustrated embodiment of FIG. 1A, is a liquid-cooled gas cooler 18 thatis cooled by a secondary, high temperature coolant loop 19. In theillustrated embodiment of FIG. 1A, liquid coolant flows through the loop19 during A/C operation (possibly at a lower mass flow rate thanrefrigerant from the air-cooled gas cooler 14) to further reduce thetemperature of the refrigerant, however, compared to the air-cooled gascooler 14, the heat load of the liquid-cooled gas cooler 18 can besmall. In other embodiments, the heat load of the liquid-cooled gascooler 18 can be substantially equal to or larger than the heat loadexperienced by the air-cooled gas cooler 14, depending upon one or moreof the relative sizes and cooling capacities of the air-cooled gascooler 14 and the liquid-cooled gas cooler 18, the mass flow rates ofrefrigerant and coolant flows through and across the air-cooled gascooler 14 and the liquid-cooled gas cooler 18, the presence or absenceof a fan 16 for the air-cooled gas cooler 14, and the types and coolingcapacities of the coolants used in the air-cooled gas cooler 14 and theliquid-cooled gas cooler 18.

As shown in FIG. 1A, from the liquid-cooled gas cooler, the refrigerantcan enter the high pressure side of a suction line heat exchanger (SLHX)20 for more cooling before going through an expansion device or valve22. After the refrigerant exits the expansion valve 22, the refrigerantcan enter an air-to-refrigerant evaporator 24. A fan (not shown) can bepositioned adjacent to or along an airflow path opening onto theevaporator 24. In some embodiments, the fan can be turned off duringperiods of reduced cooling demand and/or to limit power consumption andimprove efficiency of the refrigeration system 10. In embodiments inwhich the fan can be turned off or operated at a reduced speed, the heatduty of the evaporator 24 can be limited to far less than the heat dutyof a liquid-to-refrigerant evaporator 26 that receives the refrigerantfrom the heat exchanger 24.

In the liquid-to-refrigerant evaporator 26, the refrigerant canevaporate, receiving heat energy from and thereby cooling down a coolant(e.g., glycol, water, R12, engine coolant, any organic refrigerant,R245fa, air, and the like) flowing through the liquid-to-refrigerantevaporator 26 from another secondary, low temperature coolant loop 28.It should be noted that the air-heated evaporator 24 can be placedeither upstream or downstream of the liquid-heated evaporator 24 withrespect to the flow of the refrigerant. The same can be said of theliquid-cooled gas cooler 18 with respect to the air-cooled gas cooler14. However, it can be desirable to avoid excess heating and/or boilingof the slow moving or stagnant liquid in the liquid-cooled gas cooler 18during operation of the refrigeration system 10 in the A/C mode.

After traveling through the evaporator 26, the refrigerant can rejectheat to the high pressure refrigerant in the SLHX 20. An accumulator(not shown in FIGS. 1A-2B) can be positioned upstream of the SLHX 20 onthe low-pressure-side. This accumulator can be a separate unit, oralternatively, can be directly integrated with the SLHX 20.

In addition to the liquid-refrigerant evaporator 26, the low temperaturecoolant loop 28 can include a pump 29 for moving liquid coolant throughthe liquid side of the evaporator 26. While heat from the coolant istransferred to the refrigerant in the evaporator 26, a heat exchangercooler core 30, which can be mounted in an inside space 32, such as, forexample, the cabin of a truck or another vehicle, can operate totransfer heat away from the low temperature coolant in the coolant loop28. The cooler core 30 can be accompanied by an air mover 34, such as afan or blower, and can cool down the air inside the space 32 and/orremove humidity from the air in the space 32. In some embodiments, ifthe air stream through or across the heat exchanger 30 is cooled belowthe dew point, a small amount of liquid coolant can be circulatedthrough the hot coolant loop 19 to reheat the air entering the cabin (asshown by three dashed arrows).

FIG. 1B shows a schematic illustrating the refrigeration system 10during operation in the heating (HP) mode. As shown by three solidarrows, the refrigerant flows through the system 10 in the samedirection as described above with respect to operation in the A/C mode.However, the fan 16 adjacent to the air-cooled gas cooler 14 isdeactivated and high temperature liquid coolant is pumped through thehigh temperature coolant loop 19 by a pump 35 to provide cooling to therefrigerant in the liquid-cooled gas cooler 18. In the cold temperatureloop 28, the cold pump 29 is turned off and the air-to-refrigerant fan34 can be activated. This allows for additional heating inside of thespace 32 by the transfer of heat from the high temperature coolant tothe air flow in an air-to-coolant heat exchanger heater core 36. Toincrease the coefficient of performance (COP) of the system 10 whileoperating in HP mode during cold weather, a waste heat air stream 40from a waste heat source 42, such as a cooling system 43 for anauxiliary power unit 44 can be routed through the air-to-refrigerantevaporator 24.

In other embodiments, the waste heat source 42 and/or a different wasteheat source 42 can also or alternatively provide heat to aliquid-to-liquid heat exchanger evaporator or an integrated auxiliarypower unit (APU) stack cooler and evaporator coolant loop. In thelatter-case, the waste heat source 42 can remove the need for an extraair-heated evaporator, and the “cooler” core can add heat to the spaceair.

FIGS. 2A and 2B illustrate an alternate embodiment of a refrigerationsystem 10 according to the present invention. The refrigeration systemshown in FIGS. 2A and 2B is similar in many ways to the illustratedembodiments of FIGS. 1A and 1B described above. Accordingly, with theexception of mutually inconsistent features and elements between theembodiment of FIGS. 2A and 2B and the embodiments of FIGS. 1A and 1B,reference is hereby made to the description above accompanying theembodiments of FIGS. 1A and 1B for a more complete description of thefeatures and elements (and the alternatives to the features andelements) of the embodiment of FIGS. 2A and 2B.

FIG. 2A illustrates a simpler version of the refrigeration system 10. Inthis embodiment of the refrigeration system 10, the low temperaturefluid loop 28, the high temperature loop 19, and the coolant lines 46 ofan APU coolant system 43 are directly plumbed into each other, and onlyone liquid pump 47 (not including the APU coolant loop pump) is requiredfor the loops 19 and 28.

As shown in FIG. 2A, a matrix 48 of liquid valves 50, 52, 54, 56, 58 and59 can be used to direct the coolant flows to the desired locationduring HP and A/C modes. This allows for the elimination of theair-to-refrigerant evaporator 24, and for the functions of the coolerand heater cores 30 and 36 to be combined in one heat exchanger in theform of a heater/cooler core 60.

For example, during operation in A/C mode, by opening valve 59 (shownunshaded), closing valves 56 and 58 (shown in solid), opening valves 52and 54, and closing valve 50, the APU coolant will not enter the lowtemperature loop 28 (which is heating the evaporator 26), and no coolantwill pass to the liquid-cooled gas cooler 18 via the high temperatureloop 19, while the coolant in the low temperature loop 28 rejects heatto the refrigerant in the evaporator 26 and receives heat from the airstream passing through the heater/cooler core 60. In some applications,it may be desirable for a small amount of cold liquid to pass throughthe valve 50 and the liquid-cooled gas cooler 18. This can allow therefrigerant temperature to fall below the ambient temperature, thuspotentially improving system COP.

As shown in FIG. 2B, in HP mode, by closing or modulating the valve 59(now shown in solid), opening the valves 56 and 58 (now shown unshaded),closing the valves 52 and 54 and opening the valve 50, the APU coolantcan be directed to the liquid-to-refrigerant evaporator 26, and thencirculated directly back to the APU 44 without passing through thecombined heater/cooler core 60, while the coolant in the hightemperature loop 19 is circulated through the liquid-cooled gas cooler18 to receive heat from the refrigerant and then through theheater/cooler core 60 to reject heat to the air stream passingtherethrough.

FIGS. 3A and 3B illustrate an alternate embodiment of a refrigerationsystem 10 according to the present invention. The refrigeration systemshown in FIGS. 3A and 3B is similar in many ways to the illustratedembodiments of FIGS. 1A-2B described above. Accordingly, with theexception of mutually inconsistent features and elements between theembodiment of FIGS. 3A and 3B and the embodiments of FIGS. 1A-2B,reference is hereby made to the description above accompanying theembodiments of FIGS. 1A-2B for a more complete description of thefeatures and elements (and the alternatives to the features andelements) of the embodiment of FIGS. 3A and 3B.

The refrigeration system 10 of FIGS. 3A and 3B differs from that ofFIGS. 1A and 1B in that the air-to-refrigerant evaporator 24 has beeneliminated and replaced with an air-heated coolant heat exchanger 66that has been added to a bypass line 68 in the low temperature fluidloop 28, with a three-way valve 70 (or series of two-way valves)controlling the flow of coolant through the cooler core 30 and theambient air-heated coolant heat exchanger 66.

As shown in FIG. 3A, during operation in the A/C mode, the valve 70 candirect coolant through the cooler core 30, rather than the heatexchanger 66, so that the coolant flowing in the low temperature loop 28can absorb heat from the air flow passing through the cooler core 30.The operation of the high temperature loop can be substantially similarto the version of the system 10 in FIGS. 1A and 1B. It should beappreciated that the heat exchanger 66 could be replaced by any othertype of heat exchanger that would utilize any other heat source, suchas, for example, a liquid waste heat stream from a generator.

As shown in FIG. 3B, during operation in the HP mode, the valve 70 isused to direct the coolant through the heat exchanger 66, rather thanthrough the cooler core 30, so that heat from the ambient air passingthrough the heat exchanger 66 is transferred to the coolant flowing inthe low temperature loop 28.

FIGS. 4A and 4B illustrate an alternate embodiment of a refrigerationsystem 10 according to the present invention. The refrigeration systemshown in FIGS. 4A and 4B is similar in many ways to the illustratedembodiments of FIGS. 1A-3B described above. Accordingly, with theexception of mutually inconsistent features and elements between theembodiment of FIGS. 4A and 4B and the embodiments of FIGS. 1A-3B,reference is hereby made to the description above accompanying theembodiments of FIGS. 1A-3B for a more complete description of thefeatures and elements (and the alternatives to the features andelements) of the embodiment of FIGS. 4A and 4B.

As shown in FIGS. 4A and 4B, this system 10 differs from that of FIGS.1A and 1B in that the liquid-cooled gas cooler 14 and theair-to-refrigerant evaporator 24 have both been eliminated, thefunctions of the cooler and heater cores 30 and 36 are combined in aheater/cooler core 60 such as discussed in connection with FIGS. 2A and2B, and an air-heated coolant heat exchanger 66, such as discussed inconnection with FIGS. 3A and 3B, has been plumbed into both the hightemperature loop 19 and the low temperature loop 28 with a three-wayvalve 74 (or series of two-way valves) provided in the high temperatureloop 19 and a three-way valve 78 provided in the low temperature loop 28to control the coolant flow in both of the loops 19 and 20 through theheat exchangers 60 and 66.

As shown in FIG. 4A, during operation in the A/C mode, the valve 78directs the coolant in the low temperature loop 19 through the core 60,rather than through the heat exchanger 66, to remove heat from the cabin32, and the valve 74 directs the coolant from the high temperature loop19 through the heat exchanger 66, rather than the core 60, to rejectheat absorbed by the coolant from the gas cooler 18 to the ambient airflow through the heat exchanger 66.

As shown in FIG. 4B, during operation in the HP mode, the coolant in thehigh temperature loop 19 is directed by the valve 74 through theheater/cooler core 60, rather than through the heat exchanger 66, whilethe valve 78 in the low temperature loop 28 directs coolant through theheat exchanger 66, rather than the heater/cooler core 60, so as toabsorb heat from the ambient air flowing through the heat exchanger 68.

The embodiments described above and illustrated in the figures arepresented by way of example only and are not intended as a limitationupon the concepts and principles of the present invention. As such, itwill be appreciated by one having ordinary skill in the art that variouschanges are possible.

1. A refrigeration system having both a heating mode for providing heatto a load space and a cooling mode for removing heat from the loadspace, the system comprising: a first refrigerant circuit including afirst heat exchanger for transferring heat from refrigerant of the firstrefrigerant circuit to air; a second refrigerant circuit including asecond heat exchanger for transferring heat from air to refrigerant ofthe second refrigerant circuit; and a third refrigerant circuitincluding: a compressor for increasing pressure of refrigerant of thethird refrigerant circuit; a third heat exchanger connected to thecompressor for receiving refrigerant from the compressor, and connectedto the first refrigerant circuit such that heat exchange can occurbetween the refrigerant traveling through the first refrigerant circuitand the refrigerant traveling through the third refrigerant circuit; anexpansion device for reducing the pressure of the refrigerant of thethird refrigerant circuit; and an evaporator connected to the expansiondevice, and connected to the second refrigerant circuit such that heatexchange can occur between the refrigerant traveling through the secondrefrigerant circuit and the refrigerant traveling through the thirdrefrigerant circuit, the refrigerant traveling along the thirdrefrigerant circuit in a common direction during operation in both theheating mode and the cooling mode; wherein refrigerant is prevented frommoving between the first refrigerant circuit, the second refrigerantcircuit, and the third refrigerant circuit during operation in theheating and cooling modes.
 2. The refrigeration system of claim 1,wherein the third heat exchanger is a liquid-cooled gas cooler.
 3. Therefrigeration system of claim 2, further comprising an air-cooled gascooler connected in series with the liquid-cooled gas cooler and to atleast one of the compressor and the expansion device.
 4. Therefrigeration system of claim 1, wherein the evaporator is aliquid-heated evaporator.
 5. The refrigeration system of claim 4,further comprising an air-heated evaporator connected in series with theliquid heated evaporator and to at least one of the expansion device andthe compressor.
 6. The refrigeration system of claim 1, furthercomprising a suction line heat exchanger connected to the third heatexchanger, the expansion valve, the evaporator, and the compressor alongthe third refrigerant circuit.
 7. The refrigeration system of claim 1,wherein the refrigerant of the third refrigerant circuit is carbondioxide.
 8. The refrigeration system of claim 1, wherein the first heatexchanger and the second heat exchanger are combined in a single heatexchanger.
 9. The refrigeration system of claim 1, further comprising aheat source separate from the first, second, and third refrigerantcircuits for providing heat to the refrigeration system during operationin the heating mode.
 10. A refrigeration system having both a heatingmode for providing heat to a load space and a cooling mode for removingheat from the load space, the refrigeration system comprising: a firstrefrigerant circuit extending between a compressor, an evaporator, anexpansion device, and a first heat exchanger, the first refrigerantcircuit defining a flow path for a refrigerant traveling in a directionalong the refrigerant circuit during operation of the refrigerationsystem in the heating mode and the cooling mode; a second refrigerantcircuit extending between the condenser and a second heat exchanger, thesecond refrigerant circuit including a first refrigerant pump; and athird refrigerant circuit extending between the evaporator and thesecond heat exchanger, the third refrigerant circuit including a secondrefrigerant pump, the second refrigerant pump being operational duringoperation in the heating mode and being idle during operation in thecooling mode.
 11. The refrigeration system of claim 10, wherein thesecond refrigerant circuit is separated from the first refrigerantcircuit such that refrigerant is prevented from moving between the firstand second refrigerant circuits, the second refrigerant circuitextending through the first heat exchanger such that heat exchange canoccur between the refrigerant traveling through the first refrigerantcircuit and a refrigerant traveling through the second refrigerantcircuit.
 12. The refrigeration system of claim 10, wherein the thirdrefrigerant circuit is separated from the first refrigerant circuit suchthat refrigerant is prevented from moving between the first and thirdrefrigerant circuits, the third refrigerant circuit extending throughthe evaporator such that heat exchange can occur between the refrigeranttraveling through the first refrigerant circuit and a refrigeranttraveling through the third refrigerant circuit.
 13. The refrigerationsystem of claim 10, wherein the first refrigerant circuit includes asuction line heat exchanger.
 14. The refrigeration system of claim 10,wherein the second heat exchanger includes a first heat exchanger coreand a second heat exchanger core, the first heat exchanger core beingassociated with the second refrigerant circuit, the second heatexchanger core being associated with the third refrigerant circuit. 15.The refrigeration system of claim 10, further comprising a heat sourceseparate from the first, second, and third refrigerant circuits forproviding heat to the refrigeration system during operation in theheating mode.
 16. The refrigeration system of claim 10, wherein theevaporator is a liquid-heated evaporator and the first heat exchanger isa liquid-cooled gas cooler.
 17. The refrigeration system of claim 16,further comprising an air-cooled gas cooler connected in series with theliquid-cooled gas cooler.
 18. The refrigeration system of claim 16,further comprising an air-heated evaporator connected in series with theliquid-heated evaporator.
 19. A method of operating a refrigerationsystem, the method comprising the acts of: directing a refrigerant alonga refrigerant circuit in a direction between a compressor, anevaporator, an expansion device, and a first heat exchanger duringoperation of the refrigeration system in a cooling mode; operating afirst pump when the refrigeration system is operating in the coolingmode to circulate refrigerant through a second heat exchanger;transferring heat from a load space to the refrigerant in therefrigerant circuit when the refrigeration system is operating in thecooling mode; stopping the first pump when the refrigeration system isoperating in a heating mode; directing the refrigerant along therefrigerant circuit in the direction during operation of therefrigeration system in the heating mode; operating a second pump whenthe refrigeration system is operating in the heating mode to circulaterefrigerant through the second heat exchanger in heat exchange relationwith the refrigerant of the refrigerant circuit; and transferring heatto the load space from the refrigerant in the refrigerant circuit whenthe refrigeration system is operating in the heating mode.
 20. Themethod of claim 19, further comprising heating the refrigerant with aheat source separate from the refrigerant circuit when the refrigerationsystem is operating in the heating mode.
 21. The method of claim 19,further comprising cooling the refrigerant using a suction line heatexchanger included along the refrigerant circuit.
 22. The method ofclaim 19, further comprising heating the refrigerant with an air-heatedevaporator and a liquid-heated evaporator when the refrigeration systemis operating in the cooling mode.
 23. The method of claim 19, furthercomprising cooling the refrigerant with an air-cooled condenser and aliquid-cooled condenser when the refrigeration system is operating inthe heating mode.